Light-emitting device and electric appliance

ABSTRACT

An inexpensive light emitting device capable of displaying a bright image and an electric appliance using the light emitting device. In the light emitting device having a pixel portion and a driver circuit formed on one insulating member, all of semiconductor elements for the pixel portion and the driver circuit are formed by n-channel semiconductor elements, thereby enabling the manufacturing process to be simplified. Each of light-emitting elements provided in the pixel portion emits light in such a direction that most of the light travels away from the insulating member, so that substantially the whole of the pixel-forming segment electrode (corresponding to a cathode of an EL element) is formed as an effective light-emitting area. Therefore, a low-priced light-emitting device capable of displaying a bright image can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device which includesan insulating member, a pixel portion and driver circuits for supplyingsignals to the pixel portion, and in which the pixel portion and thedriver circuits are formed on the same insulating member. Specifically,the present invention includes techniques effective in improving adevice having an element constituted of a pair of electrodes and a thinfilm of a light-emitting material interposed between the pair ofelectrodes (which element will be hereinafter referred to as“light-emitting element”) (which device will be hereinafter referred toas “light-emitting device”). The light-emitting device of the presentinvention covers an organic electro-luminescent (EL) display and anorganic light-emitting diode (OLED).

In particular, the present invention includes techniques effective inimproving a device having an element constituted of an anode, a cathode,and a thin film of a light-emitting material capable ofelectroluminescence and interposed between the pair of electrodes (whichthin film will be hereinafter referred to as “EL film”) (which elementwill be hereinafter referred to as “EL element”) (which device will behereinafter referred to as “EL light-emitting device”).

Light-emitting materials usable in the present invention comprise all oflight-emitting materials capable of emitting light (phosphorescenceand/or fluorescence) by singlet excitation, triplet excitation, or bothof singlet and triplet excitation.

The present invention can also be applied to a device having an elementin which a liquid crystal material is interposed between electrodes(which element will be hereinafter referred to as “liquid crystalelement”) (which device will be hereinafter referred to as “liquidcrystal display device”).

2. Description of the Related Art

In recent years, the development of active-matrix EL light-emittingdevices have been promoted. In active-matrix EL light-emitting devices,thin-film transistors (hereinafter referred to as “TFTs”) are providedin each of pixels (EL elements) of the pixel portion, and the currentcaused to flow through each EL element is controlled through the TFTs tocontrol the luminance of the pixel. Therefore, voltages can be uniformlysupplied to the pixels even if the number of pixels to be formed by thepixel portion is increased. For this reason, active-matrix ELlight-emitting devices are suitable for forming a high-definition image.

Active-matrix EL light-emitting devices also have the advantage thatcircuits including a shift register and a latch or a buffer constitutingdriver circuits for transmitting signals to the pixel portion can beformed by TFTs on one insulating member on which the pixel portion isalso formed. Therefore, when an EL light-emitting device of thisstructure is manufactured, it can be designed so as to be remarkablysmall in size and weight.

Active-matrix EL light-emitting devices, however, have a drawback inthat a complicated TFT fabrication process increases the manufacturingcost of the device. Moreover, since a plurality of TFTs are formedsimultaneously, the manufacturing process may be so complicated that itis difficult to ensure a satisfactory yield. In particular, an operationfailure in the driver circuits may result in a line defect such that onerow of pixels do not operate.

FIGS. 18A and 18B show the basic structure of an active-matrix ELlight-emitting device. Referring to FIG. 18A, a TFT 1802 for controllinga current flowing through an EL element (hereinafter referred to as“current control TFT”) is formed on a substrate 1801, and an anode 1803is connected to the current control TFT 1802. An organic EL film (thinfilm of a light-emitting organic material capable of producingelectroluminescence) 1804 and a cathode 1805 are formed on the anode1803. Thus, an EL element 1806 constituted of the anode 1803, theorganic EL film 1804 and the cathode 1805 is formed.

In this light-emitting EL device, light produced in the organic EL film1804 passes through the anode 1803 to travel in the direction of thearrow indicated in the figure. The current control TFT 1802 acts as ashielding such as to block light emitted to travel to an observer and tocause a reduction in the effective emission region (a region throughwhich the observer can observe emission of light). If the effectiveemission region is reduced, a need arises to increase the intensity oflight emitted from the organic EL film in order to obtain a brightimage. This can be achieved by increasing the voltage at which theorganic EL element film is driven. However, if the drive voltage isincreased, there is apprehension that the degradation the organic ELelement film is promoted.

An active-matrix EL light-emitting device of a structure such as shownin FIG. 18B, designed to solve this problem, has been proposed.Referring to FIG. 18B, a current control TFT 1807 is formed on asubstrate 1801, and a cathode 1808 is connected to the current controlTFT 1807. An organic EL film 1809 and an anode 1810 are formed on thecathode 1808. Thus, an EL element 1811 constituted of the cathode 1808,the organic EL film 1809 and the anode 1810 is formed. That is, thestructure of the EL element 1811 is in an inverse directionalrelationship with that of the EL element 1806 shown in FIG. 18A.

In this active-matrix EL light-emitting device, most of light travelingto the cathode 1808 side after being produced by the organic EL film1809 is reflected by the cathode 1808 to be emitted through the anode1810 in the direction arrow indicated in the figure. Therefore, thewhole of the region where the cathode 1808 is formed can be used as aneffective light-emitting region, so that an active-matrix ELlight-emitting device having a high light extraction efficiency can beobtained. Further, even if the drive voltage is low, a high intensity ofemitted light can be obtained to provide a bright image.

SUMMARY OF THE INVENTION

In view of the above-described circumstances, an object of the presentinvention is to provide a light-emitting device having a high lightextraction efficiency and designed so as to be manufactured at a lowcost.

Another object of the present invention is to provide a light-emittingdevice low-priced but capable of displaying a bright image.

Still another object of the present invention is to provide a low-pricedelectric appliance using the light-emitting device of the presentinvention in its display portion and therefore capable of displaying abright image.

The inventors of the present invention have conceived that it isdesirable to use an n-channel TFT as a current control TFT in the caseof manufacturing an EL light-emitting device having a high lightextraction efficiency as shown in FIG. 18B to have a high lightextraction efficiency. The reason for this conception will be explainedwith reference to FIGS. 19A and 19B.

FIG. 19A shows an example of use of a p-channel TFT 1901 as the currentcontrol TFT in the structure shown in FIG. 18B. The current control TFT1901 has its source connected to a current supply line 1902 and itsdrain connected to the cathode of an EL element 1903. In this structure,it is necessary to set the potential of the current supply line 1902 toV_(L) (low-level potential equal to ground potential in this example)and to set the potential of the anode of the EL element 1903 to V_(H)(high-level potential of 5 to 10 V in this example).

The potential of the gate of the current control TFT 1901 is V_(G), thepotential of the source is V_(S), and the potential of the drain isV_(D). Then the current control TFT 1901 has a gate voltage expressed asV_(G)-V_(S), a voltage between the source and the drain as V_(D)-V_(S),a source voltage as V_(S)-V_(L), and a drain voltage as V_(D)-V_(L).V_(S) corresponds to the potential of the cathode of the EL element1903. When the gate of the current control TFT 1901 is opened, thepotential of the current supply line 1902 become closer to V_(L). Thepotential V_(D) of the drain is equal to the potential V_(L) of thecurrent supply line 1902.

In the case of the structure shown in FIG. 19A, potential V_(S) changes(becomes closer to V_(L)) when the current control TFT 1901 is opened.Under this condition, the gate voltage (V_(G)-V_(S)) and the voltage(V_(D)-V_(S)) between the source and the drain themselves change. As aresult, the current flowing through the current control TFT 1901 changeswith the change in V_(S) and there is a problem of failure to supply thecurrent to the EL element 1903 with stability.

FIG. 19B shows an example of use of a current control TFT as then-channel TFT in the structure shown in FIG. 18B. In this case, thepotential V_(S) of the source of the current control TFT 1904 is alwaysequal to the potential V_(L) of the current supply line 1902, so thatthe gate voltage (V_(G)-V_(S)) and the voltage (V_(D)-V_(S)) between thesource and the drain do not change. Therefore, a current can be suppliedto the EL element 1903 with stability.

From the above-described facts, the inventors of the present inventionhave understood that in a case where a pixel is formed as the structurein which the cathode of the EL element is connected to the drain of thecurrent control TFT, it is desirable to use an n-channel TFT as thecurrent control TFT.

The present invention achieved with this understanding is characterizedin that all semiconductor elements (typically, thin-film transistors)are formed as n-channel semiconductor elements in order to reduce themanufacturing cost of the active-matrix light-emitting device. Thenumber of the steps for fabricating p-channel semiconductor elements arereduced to simplify the process of manufacturing the light-emittingdevice and to enable the light-emitting device to be manufactured at alower cost.

The present invention is also characterized by forming driver circuitsonly of n-channel semiconductor elements. That is, according to thepresent invention, only n-channel semiconductor elements are combined toform a driver circuit while ordinary driver circuits are designed on thebasis of a complementary metal-oxide semiconductor (CMOS) circuit inwhich an n-channel semiconductor element and a p-channel semiconductorelement are complementarily combined.

FIG. 1 shows an active-matrix EL light-emitting device in an embodimentof the present invention in which a pixel portion and driver circuitsfor transmitting signals to the pixel portion are formed on oneinsulating member.

Referring to FIG. 1, an insulating film 12 is formed as a base on asubstrate 11, and a TFT 201 which operates as a switching device(hereinafter referred to as “switching TFT”), a TFT 202 which operatesas a current-control element (hereinafter referred to as “currentcontrol TFT”), an n-channel TFT 203, and an n-channel TFT 204 are formedon the insulating film 12. The switching TFT 201 and the current controlTFT 202 are illustrated as an example of TFTs provided in the pixelportion while the n-channels TFT 203 and 204 are illustrated as anexample of semiconductor elements in an inverter circuit provided in adriver circuit.

The present invention comprises techniques particularly effective informing the light-emitting device on a plastic substrate (including aplastic film) used as a substrate 11. Presently, no techniques forenabling p-channel TFTs formed on a plastic substrate to havesatisfactory electrical characteristics are available. Therefore, thepresent invention comprising forming all the TFTs as n-channel TFTs isparticularly effective in fabricating an active-matrix EL light-emittingdevice on a plastic substrate.

The pixel portion will first be described. The switching TFT 201 is ann-channel TFT which includes an active layer containing a source region13, a separation region (impurity region existing between channelforming regions) 14, a separation region 15, a drain region 16, andchannel forming regions 17 to 19, a gate insulating film 20, gateelectrodes 21 a to 21 c, an inorganic insulating film 22, an organicinsulating film 23, source wiring 24, and drain wiring 25. The switchingTFT 201 is a switching element for controlling the gate voltage of thecurrent control TFT.

The inorganic insulating film 22 is a silicon nitride film or a siliconoxynitride (represented by SiOxNy), and the organic insulating film 23is a resin film (polyimide film, acrylic resin film, polyamide film, orbenzocyclobutene film). Metal particles or carbon particles may bedispersed in the organic insulating film 23. In such a case, the contentof metal particles or carbon particles may be adjusted so that thespecific resistance is 1×10⁸ to 1×10¹⁰ Ωm thereby limiting occurrence ofstatic electricity.

Preferably, a metallic film containing an element belonging to the group1 or 2 in the periodic table (preferably, cesium, magnesium, lithium,calcium, potassium, barium or beryllium) is used for the source wiring24 and the drain wiring 25. The metallic film is, preferably, aluminumfilm, copper film or silver film. Bismuth film may also be used as themetallic film.

The current control TFT 202 is an n-channel TFT which includes an activelayer containing a source region 26, a drain region 27, and a channelforming region 28, gate insulating film 20, a gate electrode 29,inorganic insulating film 22, organic insulating film 23, source wiring30, and a pixel electrode 31. A drain wiring 25 portion extending fromthe switching TFT 201 is connected to the gate electrode 29 of thecurrent control TFT 202. The pixel electrode 31 connected to the drainregion 27 of the current control TFT 202 functions as a cathode of an ELelement 40.

Preferably, a metallic film containing an element belonging to the group1 or 2 in the periodic table (preferably, cesium, magnesium, lithium,calcium, potassium, barium or beryllium) is used to form the pixelelectrode 31. The metallic film is, preferably, aluminum film, copperfilm or silver film. Bismuth film may also be used as the metallic film.

Needless to say, the source wiring 24 and the drain wiring 25 for theswitching TFT 201 and the source wiring 30 for the current control TFT202 are formed simultaneously with the pixel electrode 31, so that thesame material as that of the pixel electrode 31 is used to form thewiring.

A bank 32 is also formed which is a resin film (polyimide film, acrylicresin film, polyamide film, or benzocyclobutene film) containing metalparticles or carbon particles such that the specific resistance is 1×10⁸to 1×10¹⁰ Ωm. If the specific resistance is within this range, it ispossible to reduce occurrence of electrostatic breakdown of the TFT atthe time of film forming. A thin film 33 comprising an organic EL filmand an anode 34 of the EL element 40 (typically, an electrode formed ofan oxide conductive film) are also provided.

Further, a passivation film 36 is formed so as to cover the EL element40 formed of the pixel electrode (cathode) 31, the thin film 33,comprising an organic EL film, and the anode 34. To form the passivationfilm 36, silicon nitride film, silicon oxynitride film, carbon film(preferably, diamond-like carbon film), aluminum oxide film or tantalumoxide film may be used. A multilayer film formed of a combination ofsome of these films may be formed.

FIGS. 2A and 2B show the circuit configuration of one pixel-formingsegment in the pixel portion. Referring to FIG. 2A, a gate wiring line205 is provided to apply a gate voltage to the gate electrodes 21 a to21 c of the switching TFT 201, and a current supply line 206 is providedto supply a current which flows through the EL element 40. A capacitor207 is provided to hold a gate voltage applied to the gate electrode 29of the current control TFT 202. The source wiring 30 portion at thecurrent control TFT 202 is set to a low-level potential (V_(L)) whilethe anode 34 of the EL element is set to a high-level potential (V_(H)).

FIG. 2B shows another example of the circuit configuration of one pixel.In the circuit configuration shown in FIG. 2B, an EL element 208 isformed between the current supply line 206 and the current control TFT202. In this case, the source wiring portion 30 at the current controlTFT 202 is set to a high-level potential (V_(H)) while the anode 34 ofthe EL element is set to a low-level potential (V_(L)). Also, thecurrent supply line 206 functions as the anode 34 of the EL element.

Examples of the circuit having two TFTs (one switching TFT and onecurrent control TFT) for one pixel have been described. However, thenumber of TFTs may be three, four, five, six or more. That is, it ispossible to provide TFTs for control signals other than a video signalin addition to the switching TFT for changing the video signal inputfrom the source wiring 24 and the current control TFT for controllingthe amount of current flowing through the EL element 40.

The driver circuit will next be described with reference to FIG. 1. Then-channel TFT 203 includes an active layer containing a source region41, a drain region 42, and a channel forming region 43, gate insulatingfilm 20, a gate electrode 44, inorganic insulating film 22, organicinsulating film 23, source wiring 45, and drain wiring 46.

The n-channel TFT 204 includes an active layer containing a sourceregion 47, a drain region 48, and a channel forming region 49, gateinsulating film 20, a gate electrode 50, inorganic insulating film 22,organic insulating film 23, source wiring 51, and drain wiring 46 commonto the n-channel TFTs 203 and 204.

The source wiring 45 for the n-channel TFT 203, the drain wiring 46(common to the n-channel TFTs 203 and 204) and the source wiring 51 forthe n-channel TFT 204 are formed of the same material as the pixelelectrode 31.

Each of the TFTs in this embodiment mode is formed as an enhancementtype of n-channel TFT (hereinafter referred to as “E-type NTFT”.)However, one of the n-channel TFTs 203 and 204 may be formed as adepletion type. In such a case, an element belonging to the group 15 inthe periodic table (preferably, phosphorus) or an element belonging tothe group 13 in the periodic table (preferably, boron) may be added tothe semiconductor in the channel forming region to selectively fabricatethe enhancement type and depletion type.

In a case where an NMOS circuit is formed by combining the n-channelTFTs 203 and 204, it is formed as a combination of enhancement-type TFTs(hereinafter referred to as “EEMOS circuit”) or a combination ofdepletion-type and enhancement-type TFTs (hereinafter referred to as“EDMOS circuit”).

FIG. 3A shows an example of the EEMOS circuit, and FIG. 3B shows anexample of the EDMOS circuit. Each of components 301 and 302 shown inFIG. 3A is an E-type NTFT. Components 303 and 304 shown in FIG. 3B arean E-type NTFT and a depletion type of n-channel TFT (hereinafterreferred to as “D-type NTFT”), respectively.

In FIGS. 3A and 3B, V_(DH) designates a power supply line to which apositive voltage is applied (positive power supply line), and V_(DL)designates a power supply line to which a negative voltage is applied(negative power supply line). The negative power supply line may be aground-potential power supply line (grounded power supply line).

FIGS. 4A and 4B show an example of a shift register formed by using theEEMOS circuit shown in FIG. 3A or the EDMOS circuit shown in FIG. 3B.Portions 400 and 401 of FIG. 4A are flip-flop circuits. Components 402and 403 are E-type NTFTs. A clock signal (CL) is input to the gate ofthe E-type NTFT 402, and a clock signal (CL-bar) of the oppositepolarity is input to the gate of the E-type NTFT 403. A symbol indicatedby 404 represents an inverter circuit. To form this inverter circuit,the EEMOS circuit shown in FIG. 3A or the EDMOS circuit shown in FIG. 3Bis used, as shown in FIG. 4B.

According to the embodiment mode of the present invention, all the TFTsare formed as n-channel TFTs so that the need for the process steps forforming p-channel TFTs is simplified, thereby simplifying the process ofmanufacturing the EL light-emitting device. The yield of themanufacturing process is thereby improved and the manufacturing cost ofthe EL light-emitting device can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the structure of a light-emittingdevice;

FIGS. 2A and 2B are diagrams each showing the configuration of a circuitin the pixel portion of the light-emitting device shown in FIG. 1;

FIGS. 3A and 3B are diagrams each showing the configuration of an NMOScircuit;

FIGS. 4A and 4B are diagrams showing the configuration of a shiftregister;

FIGS. 5A to 5E are diagrams showing process steps for fabricating an ELlight-emitting device;

FIGS. 6A to 6D are diagrams showing process steps for fabricating the ELlight-emitting device;

FIG. 7 is a diagram showing process steps for fabricating the ELlight-emitting device;

FIG. 8 is a diagram showing the configuration of circuit blocks of theEL light-emitting device;

FIG. 9 comprises a top view and a cross-sectional view of an example ofthe structure of the EL light-emitting device;

FIG. 10 comprises a top view and a cross-sectional view of anotherexample of the structure of the EL light-emitting device;

FIGS. 11A, 11B, and 11C are diagrams showing process steps forfabricating the EL light-emitting device;

FIG. 12 is a diagram showing the configuration of a gate-side drivercircuit;

FIG. 13 is a diagram forming a timing chart of decoder input signals;

FIG. 14 is a diagram showing the configuration of a source-side drivercircuit;

FIG. 15 is a diagram showing the configuration of a gate-side drivercircuit;

FIG. 16 is a diagram showing the configuration of a source-side drivercircuit;

FIGS. 17A and 17B are diagram s showing examples of the configuration ofthe pixel portion;

FIGS. 18A and 18B are diagrams showing examples of the structure ofconventional EL light-emitting devices:

FIGS. 19A and 19B are diagrams showing examples of the configuration ofa TFT in a pixel-forming segment;

FIGS. 20A through 20F are diagrams showing examples of electricappliances; and

FIGS. 21A and 21B are diagrams showing examples of electric appliances.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

In this embodiment, the method of manufacturing the pixel portion andthe driver circuit to be formed in the periphery thereof on the sameinsulating body is explained. However, to simplify the explanation, theNMOS circuit combining the n-channel TFT in regards to the drivercircuit is shown.

As shown in FIG. 5A, first an insulator 501 made of plastic is prepared.In this embodiment, as an insulator 501 made of plastic, an insulatorcoated with protecting films (carbon film, specifically a diamond-likecarbon film) 501 b and 501 c on both sides (the front surface and theback surface) of a plastic substrate 501 a is prepared.

Next, a base film 502 is formed covering the insulator 501 with athickness of 300 nm. In this embodiment, a silicon nitride oxide film islaminated by a sputtering method to form the base film 502. At thistime, a nitrogen concentration of layers contacting the insulator 501 ismade to be 10 to 25 wt %, and nitrogen may be included higher than otherlayers.

On the base film 502 is formed an amorphous semiconductor film (notshown) with a thickness of 50 nm by a sputtering method. Since theinsulator 501 is plastic, the film formation temperature desirably doesnot exceed 200° C. (preferably 150° C.).

Note that, there is no need to limit to the amorphous semiconductorfilm, provided that the semiconductor film includes the amorphousstructure (includes a microcrystalline semiconductor film). As anamorphous semiconductor film, an amorphous silicon or an amorphoussilicon germanium film may be used with the thickness of 20 to 100 nm.

Then a known laser crystallization technique for a process ofcrystallizing the amorphous semiconductor film is performed to form acrystalline semiconductor film 503. Note that, in this embodiment asolid laser (specifically, a second harmonic of a Nd: YAG laser) isused, but an excimer laser may be used. Further, the crystallizationtechnique may be any method in a range that heat resistance of theinsulator 501 made of plastic allows.

Next, as shown in FIG. 5B, the crystalline semiconductor film 503 isetched by the first photolithography step, forming island shapesemiconductor layers 504 to 507. These are semiconductor films to becomeactive layers of the TFT later on.

Note that, in this embodiment the crystalline semiconductor film is usedas active layers of the TFT, but an amorphous semiconductor film may beused as the active layers. Now, in this embodiment a protecting film(not shown) is formed from a silicon oxide film on semiconductor layers504 to 507 to a thickness of 130 nm by a method of sputtering. Impurityelements with a p-type semiconductor (hereinafter referred to as p-typeimpurity element) is added to semiconductor films 504 to 507. As thep-type impurity element, an element belonging to group 13 of theperiodic table (typically boron or gallium) may be used. Note that, theprotecting film is provided so that the crystalline silicon film is notdirectly exposed to plasma when the protecting film is added withimpurity and that minute concentration control is made possible.

Note that, the concentration of the p-type impurity element added atthis time is 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typically 1×10¹⁶ to 1×10¹⁷atoms/cm³). The p-type impurity element added with this concentration isused to regulate the threshold voltage of the n-channel TFT.

Next, the surface of the semiconductor films 504 to 507 are cleaned.First, the surface is cleaned using pure water containing ozone. Since athin oxide film is formed on the surface, then the thin oxide film isremoved using a fluoro solution diluted to 1%. With this processing, thecontaminants stuck onto the surface of the semiconductor films 504 to507 may be removed. The concentration of ozone is preferably 6 mg/L ormore. The series of steps is performed without exposure to the air.

The gate insulating film 508 is formed covering the semiconductor films504 to 507 by the sputtering method. As a gate insulating film 508, aninsulating film containing silicon with a thickness of 10 to 200 nm,preferably 50 to 150 nm may be used. This may be a single layerstructure or a lamination layer structure. In this embodiment, a siliconnitride oxide film with a thickness of 115 nm is used.

In this embodiment, the cleaning of the surface of the semiconductorfilms 504 to 507 to the formation of the gate insulating film 508 isperformed without exposure to the air, and the contamination andinterface levels are reduced in the interface of the semiconductor films504 to 507 and the gate insulating film 508. In this case, an apparatusof a multi-chamber method (or an in-line method) having at least acleaning room and a sputtering room may be used. Then, as a firstconductive film 509 a tantalum nitride film with a thickness of 30 nmand further as a second conductive film 510 a tungsten film with athickness of 370 nm are formed. In this embodiment, a combination of atungsten film as the first conductive film and an aluminum alloy film asthe second conductive film, or a combination of a titanium film as afirst conductive film and a tungsten film as a second conductive filmmay be used. These metal films may be formed by a sputtering method.Further, if inert gas such as Xe and Ne are added as sputtering gas, thefilm peeling due to stress can be prevented. Further, the purity oftungsten target may be made 99.9999% to form a low resistance tungstenfilm with a resistivity of 20 μΩcm or less. Note that, it is possible toperform the above described surface cleaning of semiconductor films 504to 507 to the formation of the second conductive film 510 withoutexposure to the air. In this case, an apparatus with a multi-chambermethod (or an in-line method) having at least a cleaning room, asputtering room for forming an insulating film and a sputtering room forforming a conductive film may be used.

Next, the resist masks 511 a to 511 g are formed and the firstconductive film 509 and the second conductive film 510 are then etched.Note that in this specification, the etching process is referred to asthe first etching process (See FIG. 5C).

In this embodiment, an ICP (Inductively Coupled Plasma) etching methodis used. Thereafter, a mixture of gases of carbon tetrafluoride (CF₄)gas, chlorine (Cl₂) gas and oxygen (O₂) gas are used as the etchinggases, under a pressure of 1 Pa. The gas flow rate of each gas is set as2.5×10⁻⁵ m³/min for carbon tetrafluoride gas, 2.5×10⁻⁵ m³/min forchlorine gas, and 1.0×10⁻⁵ m³/min for oxygen gas.

An RF power (13.56 MHz) of 500 W is applied to a coil type electrodeunder this state to generate plasma. Further, an RF power (13.56 MHz) of150 W is applied as a self bias voltage to the stage where the substrateis on so that a negative self bias is applied to the substrate. Theetching condition, is referred to as the first etching condition.

Thus, the second conductive film (tungsten film) 510 is selectivelyetched. Since oxygen is added to the etching gas, the progress of theetching of the first conductive film (tantalum nitride film) becomesextremely slow. Further, utilizing regression of the resist masks 511 ato 511 e, the shape becomes a taper shape having a taper angle of 15 to45°. With the first etching condition, a taper angle of 25° may beobtained.

Note that, taper refers to a portion where the end surface of the endportion of the electrode is oblique, and the angle with the base iscalled the taper angle. Further, the taper shape refers to a shape wherethe electrode end portion has become oblique with a taper angle, and atrapezoid is included in the taper shape.

Next, etching is performed using as the etching gas a mixture gas ofcarbon tetrafluoride gas and chlorine gas. At this time, the pressure is1 Pa, the flow rate of each gas is set as 3.0×10⁻⁵ m³/min for bothcarbon tetrafluoride gas and chlorine gas. Further, an RF power of 500 Wis applied to a coil type electrode, an RF power of 20 W is applied as aself bias voltage to the stage where the substrate is on. This conditionis referred to as the second etching condition.

In this way, gate electrodes 512 to 516 and a source wiring 517 and adrain wiring 518 of the switching TFT are formed from a lamination filmof a first conductive film and a second conductive film.

Next, with the gate electrodes 512 to 516 and the source wiring 517 andthe drain wiring 518 as masks, an n-type impurity elements (in thisembodiment phosphorus) are added in a self aligning manner. The impurityregions 519 to 527 formed in this way contain n-type impurity elementsat a concentration of 1×10²⁰ to 1×10²¹ atoms/cm³ (typically 2×10²⁰ to5×10²¹ atoms/cm³). These impurity regions 519 to 527 form the sourceregion and the drain region of the n-channel TFT.

Next, an etching of gate electrodes is carried out by using the resistmasks 511 a to 511 g as is. This etching condition in the first etchingcondition, is to have a self bias voltage of 20 W. With this condition,only the second conductive film (tungsten film) is selectively etched,to form gate electrodes (hereinbelow referred to as second gateelectrodes) 528 to 532 made from the second conductive film, a sourcewiring (hereinbelow referred to as second source wirings) 533 made ofthe second conductive film, and a drain wiring (hereinbelow referred toas second drain wirings) 534 made of the second conductive film (FIG.5D).

Next, as shown in FIG. 5E, the n-type impurity element (in thisembodiment phosphorus) is added by using the resist masks 511 a to 511 gas is. In this process, the second gate electrodes 528 to 532 functionas masks, and n-type impurity regions 535 to 544 containing the n-typeimpurity element at a concentration of 2×10¹⁶ to 5×10¹⁹ atoms/cm³(typically 5×10¹⁷ to 5×10¹⁸ atoms/cm³) are formed. Note that, in thisspecification the impurity region added with the n-type impurity elementat such a concentration is referred to as the n-type impurity region(b).

Note that, as the adding condition, an accelerating voltage is set highto 70 to 120 kV (in this embodiment 90 kV) so that the phosphorus passesthrough the first conductive film and the gate insulating film to reachthe semiconductor film.

Next, as shown in FIG. 6A, the gate insulating film 508 is etched by adry etching method, to form gate insulating films 545 to 549 which areindependent from each other. Note that, in this embodiment, an exampleof etching the gate insulating film to expose the n-type impurityregions (a) 519 to 527 is shown, but a gate insulating film may remainon the surface of the n-type impurity regions (a) 519 to 527.

In this etching condition, as the etching gas, CHF₃ (carbon trifluoride)gas is made to flow at a flow amount of 3.5×10⁻⁵ m³/min, and the etchingpressure is 7.3×10³ Pa. Further, the applied power is 800 W.

At this time, the first conductive film (tantalum nitride film) issimultaneously etched, and the gate electrodes (hereinafter referred toas the first gate electrode) 550 to 554 are formed from the firstconductive film. Therefore, the EL light-emitting device shown in thisembodiment has a gate electrode with a structure of a lamination of afirst gate electrode and a second gate electrode.

Next, as shown in FIG. 6A, the first gate electrode 550 overlaps with aportions of the n-type impurity regions (b) 535 and 536 (overlapsthrough the gate insulating film 545). Namely, the n-type impurityregions (b) 535 and 536 include the regions 535 a and 536 a overlappingthe first gate electrode 550 through the gate insulating film 545, andthe regions 536 a and 536 b that do not overlap with the first gateelectrode 550 through the gate insulating film 545.

Note that, the first gate electrode 550 functions as a part of the gateelectrode, and the regions 535 a and 535 b overlapping the first gateelectrode 550 through the gate insulating film 545, are effective inreducing the hot carrier effect. Accordingly, it is possible to suppressthe deterioration due to the hot carrier effect. The abovecharacteristics are common to all TFTs.

Next, as shown in FIG. 6B, the added n-type impurity element isactivated. As an activating means, laser annealing is preferable. Ofcourse, if the heat resistivity of the plastic substrate 501 a allows amethod of lamp annealing, furnace annealing or a combination of thesewith laser annealing, it may be used. Note that, the oxygenconcentration of the treatment atmosphere at this time is preferablykept very low. This is to prevent oxidation of the gate electrode, andpreferably the oxygen concentration is 1 ppm or less.

Next, as shown in FIG. 6C, an inorganic insulating film 555 made of asilicon nitride film or a silicon nitride oxide film is formed with athickness of 50 to 200 nm. The inorganic insulating film 555 may beformed by a sputtering method.

Thereafter, hydrogenation treatment is performed by a plasma processingusing hydrogen (H₂) gas or ammonia (NH₃) gas. When hydrogenationtreatment is completed, as an organic insulating film 556, a resin filmwhich transmits visible light is formed to a thickness of 1 to 2 μm. Asa resin film, a polyimide film, a polyamide film, an acrylic resin filmor a BCB (benzocyclobuten) film may be used. Further, it is possible touse a photosensitive resin film.

Note that, in this embodiment, a lamination film of an inorganicinsulating film 555 and an organic insulating film 556 is called aninterlayer insulating film.

Next, as shown in FIG. 6D, a contact hole is formed in the interlayerinsulating film, and wirings 557 to 562 and a pixel electrode 563 areformed. Note that, in this embodiment, the wiring is a lamination filmof three layers structured with from the lower layer side, a titaniumfilm with a thickness of 50 nm, an aluminum film containing titaniumwith a thickness of 200 nm, and an aluminum film containing lithium witha thickness of 200 nm formed continuously by a sputtering method.Further, a vaporization method may be used in formation of only analuminum film containing lithium. However, in such a case continuousformation without exposure to the air is preferable. Here, it isimportant for the surface of the pixel electrode 563 to be a metalsurface with a small work function. This is because the pixel electrode563 functions as the cathode of the EL element as it is. Therefore, itis preferable at least for the surface of the pixel electrode 563 to bea metal film containing an element belonging to group 1 or 2 of theperiodic table or a bismuth (Bi) film. Further, the wirings 557 to 562are formed simultaneously with the pixel electrode 563 so that they areformed with the same conductive film.

At this time, the wirings 557 and 559 function as a source wiring of aNMOS circuit and the wiring 558 functions as a drain wiring. Further,the wiring 560 functions as a wiring electrically connecting the sourcewiring 517 and the source region of the switching TFT, and the wiring561 functions to electrically connect the drain wiring 518 and the drainregion of the switching TFT. Further, reference numeral 562 is a sourcewiring of a current control TFT (corresponds to a current supply line),and reference numeral 563 is a pixel electrode of a current control TFT.

Next, as shown in FIG. 7, an insulating film (hereinafter referred to asbank) 564 is formed for covering the end portion of the pixel electrode563. The bank 564 may be formed by patterning an insulating filmcontaining silicon with a thickness of 100 to 400 nm or an organic resinfilm. The bank 564 is formed to fill the gap between the pixels (betweenthe pixel electrodes). Further, it has an object of the organic EL filmof such as a light emitting layer formed next not to contact directlythe end portion of the pixel electrode 563.

Note that, the bank 564 is an insulating film, therefore attention isneeded for electrostatic disruption of elements at film formation. Inthis embodiment, carbon particles and metal particles are added in theinsulating film to be the material for the bank 564 in order to decreaseresistivity, and to suppress generation of static electricity. At thistime, the amount of carbon particles and metal particles added may beregulated so that the resistivity becomes 1×10⁶ to 1×10¹² Ωm (preferably1×10⁸ to 1×10¹⁰ Ωm). Next, an EL layer 565 is formed by a vapordeposition method. Note that, in this embodiment, a laminate structureof a hole injecting layer and a light emitting layer is referred to asthe EL layer. Namely, a laminate structure combining a hole injectinglayer, a hole transporting layer, a hole preventing layer, an electrontransporting layer, an electron injecting layer, and an electronpreventing layer to a light emitting layer, is defined as the EL layer.Note that, these may be an organic material or an inorganic material, ormay be a high polymer or a low polymer.

In this embodiment, first as an electron injecting layer, a lithiumfluoride (LiF) film is formed with a thickness of 20 nm, and further analuminum-quinoline complex (Alq₃) is formed with a thickness of 80 nm asa light emitting layer. Further, a dopant (typically a luminescencepigment) to become a light emission center to the light emitting layermay be added together by vapor deposition. As this dopant, an organicmaterial emitting light through a triplet excitation may be used.

Next, when the EL layer 565 is formed, an anode 566 which has a largework function and is made from an oxide conductive film which istransparent to visible light is formed to a thickness of 300 nm. In thisembodiment, an oxide conductive film with zinc oxide added with galliumoxide is formed by a vapor deposition method. Further, as other oxideconductive films, it is possible to use an oxide conductive film made ofindium oxide, zinc oxide, tin oxide or a compound of a combinationthereof. In this way, a pixel electrode (cathode) 563, and an EL element567 containing an EL layer 565 and an anode 566 are formed.

Note that, after an anode 566 is formed, it is effective to provide apassivation film 568 for covering completely the EL element 567. Apassivation film 568 is formed of an insulating film containing a carbonfilm, a silicon nitride film and a silicon nitride oxide film, and isused as a single layer or a lamination of the insulating film.

At this time, it is preferable that a film with good coverage is used asa passivation film, and it is effective to use a carbon film, especiallya DLC (diamond-like carbon) film. The DLC film may be formed in atemperature of 100° C. or less, so that it may be formed easily abovethe EL layer 565 which has low heat resistivity. Further the DLC filmhas a high blocking effect against oxygen and can suppress oxidation ofthe EL layer 565. Therefore, a problem that the EL layer 565 oxidizedwhile carrying out the sealing process to follow may be prevented.

Further, a sealing member 569 is provided on the passivation film 568and the cover member 570 is adhered thereto. As a sealing member 569, anultraviolet cured resin may be used, and it is effective to provide asubstance having a moisture absorbent effect or a substance having anoxidation prevention effect. Further, in this embodiment, as a covermember 570, carbon films (preferably diamond-like carbon films) 570 band 570 c are used for both sides of a plastic substrate (includingplastic films) 570 a.

In this way, an EL light-emitting device with a structure as shown inFIG. 7 is completed. Note that, after the bank 564 is formed, it iseffective to perform the steps continuously until the formation of thepassivation film 568 with a film formation device of a multi-chambermethod (or an in-line method) without exposure to the air. Further, itis also possible to perform continuously the steps until the covermember 570 is adhered without exposure to the air.

In this way, n-channel TFTs 601 and 602, a switching TFT (n-channel TFT)603 and a current control TFT (n-channel TFT) 604 are formed on theinsulator 501 which has a plastic substrate as its main body. Thephotolithography step needed up to this manufacturing step is fivetimes, which is less than in a normal active matrix EL light-emittingdevice.

Namely, the manufacturing processes of the TFT are greatly simplified,and improvement in yield and reduction in manufacturing cost may berealized. Further, a very flexible and light weighted EL light-emittingdevice may also be realized since the structure is such that the TFT andthe EL element are surrounded by an insulator (including the covermember) which has a plastic substrate as a main body.

Further, as explained with reference to FIG. 6A, by providing animpurity region overlapping the first gate electrode through the gateinsulating film, an n-channel TFT which has good resistance todeterioration due to the hot carrier effect may be formed. Therefore anEL light emitting device with a high reliability may be realized.

Further, the circuit structural example of an EL light-emitting deviceof this embodiment is shown in FIG. 8. Note that, in this embodiment, acircuit structure for performing digital driving is shown, whichcomprises a source side driver circuit 801, a pixel portion 806 and agate side driver circuit 807. Note that, throughout this specification,the driver circuit is a generic term including the source side drivercircuit and the gate side driver circuit.

The source side driver circuit 801 includes a shift register 802, alatch (A) 803, a latch (B) 804 and a buffer 805. Note that in the caseof an analog driving, a sampling circuit (also referred to as a transfergate or an analog switch) may be provided in place of the latches (A)and (B). Note that, the gate side driver circuit 807 is provided with ashift register 808 and a buffer 809. Note that, the shift register shownin FIG. 4 may be used as the shift registers 802 and 808.

In this embodiment, the pixel portion 806 includes a plurality of pixelsand EL elements are provided in the plurality of pixels. At this time,the cathode of the EL element is preferably electrically connected to adrain of a current control TFT.

The source side driver circuit 801 and the gate side driver circuit 807are all formed of n-channel TFTs, and all the circuits are formed withthe EEMOS circuit shown in FIG. 3A as the basic unit. As compared to theconventional CMOS circuit, the consumption power is increased somewhatbut since the EL light-emitting device using the CMOS circuit as thedriver circuit consumes about 95% of the power in its pixel portion,even if the consumption power of the driver circuit increases a littlebit by using the NMOS circuit, it is not a major problem.

Note that, although not shown, a gate side driver circuit may also beprovided on the opposite side of the gate side driver circuit 807sandwiching the pixel portion 806. In this case, both gate side drivercircuits share common gate wirings by the same structure so that thestructure is such that even if one of the driver circuits breaks, gatesignals may be sent from the other so that the pixel portion may beoperated

Note that, the above structure is realized by manufacturing TFTsfollowing the manufacturing processes shown in FIGS. 5 to 7. Further, inthis embodiment, although only the structure of the pixel portion andthe driver circuit portion is shown, it is possible to form a logicalcircuit other than the driver circuit, such as a signal dividingcircuit, a D/A converter circuit, an operational amplifier circuit, or aγ-correction circuit, on the same insulator if the manufacturing stepsof the circuits are carried out in accordance with those of thisembodiment. In addition, it is considered that a memory portion, amicroprocessor, or the like can also be formed on the same insulator.

The EL light-emitting device of this embodiment after the process ofsealing (filling) to protect the EL element is performed will beexplained with reference to FIGS. 9A and 9B. Note that, the referencesymbols used in FIGS. 5 to 8 will be referred to when necessary.

Shown in FIG. 9A is a top view of a state in which a sealing of the ELelement has been performed. FIG. 9B is a cross sectional view of FIG. 9Acut along the line A-A′. The reference numeral 801 shown as a dottedline shows a source side driver circuit, reference numeral 806 shows apixel portion, reference numeral 807 shows a gate side driver circuit.Further, reference numeral 901 shows a covering member, referencenumeral 902 shows a first seal member, reference numeral 903 shows asecond seal member, and a sealing member 907 is provided inside thefirst seal member 902 surrounded thereby.

Note that, reference numeral 904 shows a wiring for transmitting asignal input to the source side driver circuit 801 and the gate sidedriver circuit 807, which receives a video signal or a clock signal froman FPC (flexible printed circuit) 905 to be an external input terminal.Note that, here only an FPC is shown, but this FPC may be mounted with aprinted wiring substrate (PWB), or may be in the form of a TCP (tapecarrier package). Further, an IC may be mounted on the substrate by aCOG (chip on glass).

The EL light-emitting device in this specification not only refers tothe EL light-emitting device body, but also a state where FPC, TCP orPWB is mounted thereon.

Next, the cross sectional structure is described using FIG. 9B. On theinsulator 501 are formed the pixel portion 806 and the gate side drivercircuit 807. The pixel portion 806 is composed of a plurality of pixelseach including the current control TFT 604 and the pixel electrode 563that is electrically connected to the current control TFT 604. The gateside driver circuit 807 is formed using an NMOS circuit (see FIG. 3) inwhich the n-channel TFT 601 and the n-channel TFT 602 are combined.

The pixel electrode 563 functions as the cathode of the EL element. Thebanks 564 are formed at both ends of the pixel electrode 563 to therebyform the EL layer 565 and the anode 566 of the EL element on the pixelelectrode 563. The anode 566 functions also as the common wiring for allpixels, and is electrically connected to the FPC 905 through theconnection wiring 904. Further, the pixel portion 806 and the elementincluded in the gate side driver circuit 807 are all covered by theanode 566 and the passivation film 567.

Further, a covering member 901 is adhered by a first seal member 902.Note that, a spacer made of a resin film may be provided to maintain thegap between the covering member 901 and the EL element. Then, the insideof the first seal member 902 is filled with a sealing member 907. Notethat, as a first seal member 902 and a sealing member 907, an epoxyresin is preferably used. Further, the first seal member 902 ispreferably of a material which does not transmit moisture or oxygen asmuch as possible. Further, a substance having a moisture absorbenteffect or a substance having an oxidation prevention effect may becontained inside the sealing member 907.

The sealing member 907 provided for covering the EL element functions asan adhesive for adhering the covering member 901. Further, in thisembodiment, as a material of a plastic substrate 901 a constituting thecovering member 901, a FRP (fiberglass-reinforced plastics), PVF(polyvinyl fluoride), a Mylar, a polyester, or an acrylic can be used.Next, carbon films (specifically a diamond-like carbon film) 901 b and901 c as protective films are formed on both surfaces of the plasticsubstrate 901 a with a thickness of 2 to 30 nm. Such a carbon filmprevents penetration of oxygen and water as well as mechanicallyprotects the surface of the plastic substrate 901 a. Further, it ispossible to adhere a polarizing plate (typically a round polarizingplate) on the outside carbon film 901 b.

After the covering member 901 is adhere using the sealing member 907, asecond seal member 903 is provided so as to cover a side surface(exposed surface) of the sealing member 907. The second seal member 903and the first seal member 902 may be composed of the same material.

By sealing the EL element with such a structure in the sealing member907, the EL element may be completely shielded from the outside, andpenetration of substances such as moisture and oxygen that facilitatethe deterioration of the EL layer due to oxidation thereof from theoutside may be prevented. Accordingly, an EL light-emitting device witha high reliability may be obtained.

Embodiment 2

Embodiment 2 will be described with reference to FIGS. 10A and 10B withrespect to an example of a structure for enclosing an EL element, whichis different from that of the EL light-emitting device in Embodiment 1.Portions identical or corresponding to those shown in FIGS. 9A and 9Bare indicated by the same reference characters. FIG. 10B is across-sectional view taken along the line A-A′ of FIG. 10A.

In this embodiment, a plastic film 1001 a having its both surfacescoated (covered) with carbon films (specifically, diamond-like carbonfilms) 1001 b and 1001 c formed as protective films is used as aninsulating member 1001 on which TFTs and an EL element are formed. Toform carbon films 1001 b and 1001 c on the both surfaces of the plasticfilm 1001 a, a roll to roll method may be used.

By using a sealing material 907, a cover member 1002 is attached to thesubstrate with the EL element fabricated in accordance withEmbodiment 1. A plastic film similar to the plastic film 1001 a, i.e., aplastic film 1002 a having its both surfaces coated with carbon films(specifically, diamond-like carbon films) 1002 b and 1002 c formed asprotective films, is used as a cover member 1002. Further, end surfaces(edge portions) of the cover member 1002 are sealed with a secondsealing material 1003.

Embodiment 3

Embodiment 3 will be described with respect to a case where in thelight-emitting device in accordance with Embodiment 1, the n-channel TFT601 is formed as a depletion-type TFT and each of the n-channel TFT 602,the switching TFT 603 and the current control TFT 604 is formed as anenhancement-type TFT.

The portions of the light-emitting device in the state shown in FIG. 5Aare completed by the same process as that in Embodiment 1. A siliconoxide film 1101 having a thickness of 100 to 150 nm is then formed bysputtering, and a resist mask 1102 is formed on the region where then-channel TFT 601 is formed. (FIG. 11A)

Next, an element belonging to the group 13 in the periodic table (boronin this embodiment) is added to the crystalline semiconductor film 503by using the resist mask 1102. A region 1103 where boron has been addedat a concentration of 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typically, 1×10¹⁶ to1×10¹⁷ atoms/cm³) and a region 1104 where no boron has been added arethereby formed. (FIG. 11B)

Island-like semiconductor film 1105 to 1108 are thereafter formedthrough patterning of the crystalline semiconductor film. Thesemiconductor film 1105 is formed in the region 1104 where no boron wasadded while the semiconductor films 1106 to 1108 are formed in theregion where boron was added. That is, the TFT having the semiconductorfilm 1105 as an active layer has no boron contained in the channelforming region or has a low boron concentration of 5×10¹⁴ atoms/cm³ orless while the TFTs having the semiconductor films 1106 to 1108 asactive layers contain in the channel forming region boron at aconcentration of 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typically, 1×10¹⁶ to 1×10¹⁷atoms/cm³) (FIG. 11C).

Subsequently, the same process steps as those in Embodiment 1 may beperformed. In this embodiment, the n-channel TFT formed by using thesemiconductor film 1105 is a depletion-type TFT (i.e., a normally-onn-channel TFT), and the n-channel TFTs formed by using the semiconductorfilms 1106 to 1108 are enhancement-type TFTs (i.e., normally-offn-channel TFTs).

If this embodiment is carried out, the depletion-type TFT and theenhancement-type TFT formed by the above-described method can becombined to form the EDMOS circuit shown in FIG. 3B.

This embodiment has been described with respect to an example of themethod in which a TFT is formed as an enhancement type by adding boronto the semiconductor film for a shift of the threshold voltage in theplus direction, the TFT including the channel forming region to whichboron has been added. However, a TFT can also be formed as adepletion-type by adding an element belonging to the group 15 in theperiodic table (typically, phosphorus or arsenic) for a shift of thethreshold voltage in the minus direction, the TFT including the channelforming region to which the element belonging to the group 15 in theperiodic table has been added.

This embodiment can be carried out by being combined with Embodiment 1or Embodiment 2.

Embodiment 4

Embodiment 4 will be described with reference to FIGS. 12 through 14with respect to a case where all TFTs in a source-side driver circuitand a gate-side driver circuit are formed as E-type NTFTs. According tothe present invention, a decoder using only n-channel TFTs is usedinstead of a shift register.

FIG. 12 shows an example of a gate-side driver circuit. Referring toFIG. 12, a section 100 is a decoder in the gate-side driver circuit, anda section 101 is a buffer section of the gate-side driver circuit.“Buffer section” denotes a portion in which a plurality of buffers(buffer amplifiers) are integrated. Also, “buffer” denotes a circuit fordriving while preventing a subsequent stage from influencing a precedingstage.

The gate-side decoder 100 will first be described. The decoder 100 hasinput signal lines (hereinafter referred to as “selecting lines”) 102.In FIG. 12 are illustrated the selecting lines for supplying a signal A1and a signal A1-bar (of the opposite polarity relative to that of thesignal A1), a signal A2 and a signal A2-bar (of the opposite polarityrelative to that of the signal A2), . . . An and An-bar (of the oppositepolarity relative to that of the signal An). That is, it may beunderstood that 2 n selecting lines are arranged.

The number of selecting lines is determined according to the number ofgate wiring lines to which signals are supplied from the gate-sidedriver circuit. For example, if a pixel portion for video graphics array(VGA) display is provided, the number of gate wiring lines is 480 and atotal of 18 selecting lines for 9 bits (corresponding to n=9) arerequired. The selecting lines 102 transmit signals shown in the timingchart of FIG. 13. As shown in FIG. 13, according that the frequency ofA1 is 1, the frequency of A2 is 2⁻¹, the frequency of A3 is 2⁻², and thefrequency of An is 2^(−(n−1)).

A portion 103 a is a first-stage NAND circuit (also called a NAND cell),a portion 103 b is a second-stage NAND circuit, and a portion 103 c isan nth-stage NAND circuit. The requisite number of NAND circuitscorresponds to the number of gate wiring lines, i.e., n NAND circuits inthis description. That is, in the present invention, the decoder 100 isformed by a plurality of NAND circuits.

N-channel TFTs 104 to 109 are combined to form each of the NAND circuits103 a to 103 c. Actually, 2 n TFTs are used to form the NAND circuit103. The gate of each of the n-channel TFTs 104 to 109 is connected toone of the selecting lines 102 (A1, A1-bar, A2, A2-bar, . . . An,An-bar).

In the NAND circuit 103 a, the n-channel TFTs 104 to 106 each having thegate connected to one of A1, A2, . . . , An (called positive selectinglines) are connected in parallel with each other, have a common sourceconnection to a negative power supply line (V_(DL)) 110, and have acommon drain connection to an output line 71. The n-channel TFTs 107 to109 each having the gate connected to one of A1-bar, A2-bar, . . .An-bar (called negative selecting lines) are connected in series. Thesource of the n-channel TFT 109 at the circuit end is connected to apositive power supply line (V_(DH)) 112 while the drain of the n-channelTFT 107 at the other circuit end is connected to the output line 111.

In the present invention, as described above, each NAND circuit includesn n-channel TFTs connected in series and n n-channel TFTs connected inparallel. However, the n NAND circuits 103 a to 103 c differ from eachother in the combinations of the n-channel TFTs and the selecting lines.That is, only one output line 111 is selected at a time. The selectinglines are supplied with signals such that the output lines are selectedsuccessively from the end of the array of the NAND circuits.

The buffer section 101 is formed by a plurality of buffers 113 a to 113c corresponding to the NAND circuits 103 a to 103 c. However, thebuffers 113 a to 113 c may be identical in configuration.

Each of the buffers 113 a to 113 c is formed by using n-channel TFTs 114to 116. The output line 111 from the decoder is connected as an inputline to the gate of the n-channel TFT 114 (first n-channel TFT). Then-channel TFT 114 has its source connected to a positive power supplyline (V_(DH)) 117 and has its drain connected to a gate wiring 118 ledto the pixel portion. The n-channel TFT 115 (second n-channel TFT) hasits gate connected to the positive power supply line (V_(DH)) 117, itssource to a negative power supply line (V_(DL)) 119, and its drain tothe gate wiring 118, and is always on.

That is, in the present invention, each of the buffers 113 a to 113 cincludes the first n-channel TFT (n-channel TFT 114) and the secondn-channel TFT (n-channel TFT 115) connected in series with the firstn-channel TFT and has its gate connected to the drain of the firstn-channel TFT.

An n-channel TFT 116 (third n-channel TFT) has its gate connected to areset signal line (Reset), its source to the negative power supply line(V_(DL)) 119, and its drain to the gate wiring 118. The negative powersupply line (V_(DL)) 119 may be provided as a ground power supply line(GND).

In the thus-formed buffer, the channel width of the n-channel TFT 115,represented by W1, and the channel width of the n-channel TFT 114,represented by W2, are in a relationship W1<W2. The channel width is asize of the channel forming region in the direction perpendicular to thechannel length.

The buffer 113 a operates as described below. When a negative voltage isbeing applied to the output line 111, the n-channel TFT 114 is off (insuch a state that no channel is formed). On the other hand, then-channel TFT 115 is always on (in such a state that a channel isformed), so that the voltage of the negative power supply line 119 isapplied to the gate wiring line 118.

When a positive voltage is applied to the output line 111, the n-channelTFT 114 is turned on. At this time, since the channel width of then-channel TFT 114 is larger than that of the n-channel TFT 115, thepotential of the gate wiring line 118 is pulled by the output of then-channel TFT 114, so that the voltage of the positive power supply line117 is applied to the gate wiring line 118.

Thus, through the gate wiring line 118, a positive voltage (such thatthe n-channel TFT used as the pixel switching element is turned on) isoutput when a positive voltage is applied to the output line 111, and anegative voltage (such that the n-channel TFT used as the pixelswitching element is turned off) is always output when a negativevoltage is applied to the output line 111.

The n-channel TFT 116 is used as a reset switch for forcibly reducing,to a negative voltage, the potential of the gate wiring line 118 towhich a positive voltage is applied. That is, at the end of the periodfor selection of the gate wiring line 118, a reset signal is input toapply a negative voltage to the gate wiring line 118. However, then-channel TFT 116 may be omitted.

The gate wiring lines are successively selected by the gate-side drivercircuit operating as described above. FIG. 14 shows the configuration ofthe source-side driver circuit. The source-side driver circuit shown inFIG. 14 includes a decoder 121, a latch 122, and a buffer section 123.The configurations of the decoder 121 and the buffer section 123 are thesame as those in the gate-side driver circuit, and the description forthem will not be repeated.

In the source-side driver circuit shown in FIG. 14, the latch 122 isformed of a first-stage latch 124 and a second-stage latch 125. Each ofthe first-stage latch 124 and the second-stage latch 125 has a pluralityof unit sections 127 a or 127 b each formed by m n-channel TFTs 126 a to126 c. An output line 128 from the decoder 121 is connected as an inputline to the gate of each of the m n-channel TFTs 126 a to 126 cconstituting the unit section 127 a. The letter m represents anarbitrary integer.

For example, in the case of VGA display, the number of source wiringlines is 640. If m=1, 640 NAND circuits and 20 selecting lines(corresponding to 10 bits) are required. If m=8, the necessary number ofNAND circuits is 80 and the necessary number of selecting lines is 14(corresponding to 7 bits). That is, if the number of source wiring linesis M, the necessary number of NAND circuits is (M/m).

The sources of the n-channel TFTs 126 a to 126 c are respectivelyconnected to video signal lines (V1, V2, . . . Vk) 129. That is, when apositive voltage is applied to the output line 128, the n-channel TFTs126 a to 126 c are simultaneously turned on to take in correspondingvideo signals. The video signals thus taken in are held in capacitors130 a to 130 c connected to the n-channel TFTs 126 a to 126 c.

The second-stage latch 125 has a plurality of unit sections 127 b eachformed by m n-channel TFTs 131 a to 131 c. The gates of all then-channel TFTs 131 a to 131 c are connected to a latch signal line 132.When a negative voltage is applied to the latch signal line 132, then-channel TFTs 131 a to 131 c are simultaneously turned on.

The signals held by the capacitors 130 a to 130 c are then held bycapacitors 133 a to 133 c respectively connected to the n-channel TFTs131 a to 131 c and are simultaneously output to the buffer 123. Then,the signals are output to source wiring lines 134 through the buffer, asdescribed above with reference to FIG. 13. The source wiring lines aresuccessively selected by the source-side driver circuit operating asdescribed above.

Thus, the gate-side driver circuit and the source-side driver circuitare formed only by n-channel TFTs, so that all the TFTs for pixelportion and the driver circuits can be formed as n-channel TFTs. Thepresent invention can also be applied to a light-emitting device inwhich one of the source-side driver circuit and the gate-side drivercircuit is provided as an IC externally mounted (typically, in the formof a TCP or in a COG manner).

Embodiment 5

Embodiment 5 will be described with reference to FIGS. 15 and 16 withrespect to a case where each of the source-side driver circuit and thegate-side driver circuit is formed by combining E-type NTFTs and D-typeNTFTs.

FIG. 15 shows an example of the gate-side driver circuit. Referring toFIG. 15, there are provided a shift register 140, a NAND circuit section141, and a buffer section 142.

The shift register 140 is a concrete example of the shift register shownin FIG. 4. A clock signal line 143, a clock signal line 144 forsupplying a clock of the opposite polarity, a positive power supply line(V_(DH)) 150, and a ground power supply line (GND) 151 are provided.With respect to this embodiment, three flip-flop circuits 147 a to 147 care illustrated as basic units constituting the shift register 140.Actually, a plurality of flip-flop circuits more than three areconnected in series to form the shift register 140.

The flip-flop circuit 147 a in this embodiment is configured incorrespondence with the flip-flop circuit 400 shown in FIG. 4, and theflip-flop circuit 147 b is configured in correspondence with theflip-flop circuit 401. Each of the flip-flop circuits 147 a to 147 c isformed by E-type NTFTs and D-type NTFTs.

In the flip-flop circuit 147 a, an E-type NTFT 148 has its gateconnected to the clock signal line 143, and EDMOS circuits 149 a to 149c of the construction shown in FIG. 3B are formed in a configurationsuch as shown in FIG. 4. A line 150 is a positive power supply line(V_(DH)) and a line 151 is a ground power supply line (GND).

The flip-flop circuit 147 b has the same configuration as the flip-flopcircuit 147 a except that the gate of an E-type NTFT 152 is connected tothe clock signal line 144 of the opposite polarity.

An output line 153 of the flip-flop circuit 147 a and an output line 154of the flip-flop circuit 147 b are connected to a NAND circuit 155 a.Three NAND circuits 155 a to 155 c in the NAND circuit section 141 areillustrated. Actually, the NAND circuit section 141 is formed of aplurality of NAND circuits more than three. One NAND circuit is providedin correspondence with two flip-flop circuits. Each of the NAND circuits155 a to 155 c is formed by E-type NTFTs 156 and 157 and a D-type NTFT159.

In the NAND circuit 155 a, the E-type NTFT 156 has its gate connected tothe output line 153, its source to the ground power supply line 151, andits drain to the E-type NTFT 157. The E-type NTFT 157 has its gateconnected to the output line 154, its source to the drain of the E-typeNTFT 156, and its drain to an output line 158. The D-type NTFT 159 hasits source connected to a positive power supply line 160 and its gateand drain to the output line 158.

The output line 158 from the NAND circuit 155 a is connected to an EDMOScircuit (which may also be called an inverter circuit) 161 a. ThreeEDMOS circuits 161 a to 161 c in the buffer section 142 are illustrated.Actually, the buffer section 142 is formed of a plurality of EDMOScircuits more than three.

In the EDMOS circuit 161 a, an E-type NTFT 162 has its gate connected tothe output line 158, its source to a negative power supply line (V_(DL))163, and its drain to an output line 164 (corresponding to the gatewiring of the pixel portion), and a D-type NTFT 165 has its gate anddrain connected to the output line 164 and its source to the positivepower supply line 160.

FIG. 16 shows the configuration of the source-side driver circuit. Thesource-side driver circuit shown in FIG. 16 is formed by adding transfergates 165 a to 165 c to the gate-side driver circuit shown in FIG. 15,and the same circuits as those forming the shift register 140, the NANDcircuit section 141 and the buffer section 142 can be used. Thisconfiguration is intended for analog driving.

In this embodiment, two E-type NTFTs are provided in parallel in thetransfer gates 165 a to 165 c. However, this is a redundant design andis a means for improving the current supply capacity. A line 166 is avideo signal line.

In this embodiment, if digital driving is performed, the latch 122 andthe buffer section 123 shown in FIG. 14 may be provided under the NANDcircuit section 141. Conversely, to adapt the source-side driver circuitshown in FIG. 14 to analog driving, the latch 122 may be removed and thetransfer gates shown in FIG. 16 may be added as a stage following thebuffer section 123.

As described above, the gate-side driver circuit and the source-sidedriver circuit are formed only by n-channel TFTs, so that all the TFTsfor pixel portion and the driver circuits can be formed as n-channelTFTs. The present invention can also be applied to a light-emittingdevice in which one of the source-side driver circuit and the gate-sidedriver circuit is provided as an IC externally mounted.

Embodiment 6

FIGS. 17A and 17B show examples of the construction of eachpixel-forming segment in the EL light-emitting device of the presentinvention. Referring to FIG. 17A, a line 1701 is a gate wiring line, aline 1702 is a source wiring line, a line 1703 is a positive powersupply line, and a line 1704 is a negative power supply line (which maybe a ground power supply line). Components 1705 to 1708 are E-typeNTFTs, and components 1709 and 1710 are D-type NTFTs. An EL elementindicated by 1711 is connected to the E-type NTFT 1708.

In the pixel-forming structure of this embodiment, six TFTs are providedin one pixel-forming segment to form a static random access memory(SRAM). More specifically, a plurality of E-type NTFTs and a pluralityof D-type NTFTs form an SRAM. Thus, in carrying out the presentinvention, the number of TFTs included in one pixel-forming segment isnot particularly limited.

In the pixel-forming structure of this embodiment, the E-type NTFT 1705functions as a switching TFT while the E-type NTFT 1708 functions as acurrent control TFT. Also, the inverter circuit constituted by theE-type NTFT 1706 and the D-type NTFT 1709 and the inverter circuitconstituted by the E-type NTFT 1707 and the D-type NTFT 1710 arecombined to perform a memory function.

FIG. 17B shows an example of the pixel-forming structure in whichadjacent two pixels shown in FIG. 17A have a common negative powersupply line and are symmetrically arranged. In this manner, the numberof wiring lines in each pixel-forming segment can be reduced, wherebythe pixel density is increased.

The configuration of this embodiment may be combined with any ofEmbodiments 1 to 5 to carry out the present invention.

Embodiment 7

The source-side driver circuit and the gate-side driver circuit inEmbodiment 4 or 5 can also be used in a liquid crystal display device.That is, any of the EEMOS circuit shown in FIG. 3A, the EDMOS circuitshown in FIG. 3B, the shift register shown in FIG. 4, the gate-sidedriver circuit shown in FIG. 13, and the source-side driver circuitshown in FIG. 14 can be used to form a driver circuit for the liquidcrystal display device.

The liquid crystal display device may be a liquid crystal module inwhich a flexible printed circuit (FPC) is attached to a liquid crystalpanel. The liquid crystal module comprises a construction in which aprinted wiring board (PWB) is provided as a member to which the FPC isconnected. The liquid crystal module also comprises a tape carrierpackage (TCP) in which an integrated circuit (IC) is connected to anFPC. An IC may be mounted on the substrate in a chip on glass (COG)manner.

Embodiment 8

In carrying out the present invention, bottom-gate TFTs (typically,inverted stagger TFTs) may be used as well as top-gate TFTs (typically,planar TFTs). Also, MOSFETs formed on a semiconductor substrate(typically, a silicon substrate) may be used.

The configuration of this embodiment may be combined with any ofEmbodiments 1 to 7 to carry out the present invention.

Embodiment 9

The light-emitting device or the liquid crystal display device formed byimplementing this invention may be used as a display portion of variouselectrical appliances. As electrical appliances of this invention, thereare such as an image playback device with a video camera, a digitalcamera, a goggle type display (head mounted display), a car navigationsystem, a car audio, a note type personal computer, a game apparatus, aportable information terminal (such as a mobile computer, a portabletelephone, a portable game apparatus or an electronic book), and arecording medium. Specific examples of the electronic equipment areshown in FIGS. 20 and 21.

FIG. 20A shows an EL display and includes a casing 2001, a supportingbase 2002 and a display portion 2003. The light-emitting device and theliquid crystal display device of this invention may be used for thedisplay portion 2003. When using the EL light-emitting device in thedisplay portion 2003, since it is a self-light emitting type backlightis not necessary and the display portion may be made thin.

FIG. 20B shows a video camera, which contains a main body 2101, adisplay portion 2102, a sound input portion 2103, operation switches2104, a battery 2105, and an image receiving portion 2106. Thelight-emitting device and the liquid crystal display device of thisinvention can be applied to the display portion 2102.

FIG. 20C shows a digital camera, which contains a main body 2201, adisplay portion 2202, a eye contact portion 2203, and operation switches2204. The light emitting-device and the liquid crystal display device ofthis invention can be applied to the display portion 2102.

FIG. 20D shows an image playback device equipped with a recording medium(specifically, a DVD playback device), which contains a main body 2301,a recording medium (such as a CD, LD or DVD) 2302, operation switches2303, a display portion (a) 2304, a display portion (b) 2305 and thelike. The display portion (a) is mainly used for displaying imageinformation. The display portion (b) 2305 is mainly used for displayingcharacter information. The light-emitting device and the liquid crystaldisplay device of this invention can be applied to the display portion(a) and the display portion (b). Note that, the image playback deviceequipped with the recording medium includes devices such as CD playbackdevice, and game machines.

FIG. 20E shows a portable (mobile) computer, which contains a main body2401, a display portion 2402, an image receiving portion 2403, operationswitches 2404 and a memory slot 2405. The light-emitting device and theliquid crystal display device of this invention can be applied to thedisplay portion 2402. This portable computer may record information to arecording medium that has accumulated flash memory or involatile memory,and playback such information.

FIG. 20F shows a personal computer, which contains a main body 2501, acasing 2502, a display portion 2503, and a keyboard 2504. Thelight-emitting device and the liquid crystal display device of thisinvention can be applied to the display portion 2503.

The above electronic appliances more often display information sentthrough electron communication circuits such as the internet or the CATV(cable television), and especially image information display isincreasing. When using the EL light-emitting device in the displayportion, since the response speed of the EL light-emitting device isextremely fast, it becomes possible to display pictures without delay.

Further, since the light emitting portion of the EL light-emittingdevice consumes power, it is preferable to display information so thatthe light emitting portion is as small as possible. Therefore, whenusing the EL light-emitting device in the portable information terminal,especially in the display portion where character information is mainlyshown in a cellular phone or a car audio, it is preferable to drive sothat the character information is formed of a light emitting portionwith the non-light emitting portion as a background.

Here, FIG. 21A shows a portable telephone, and reference numeral 2601shows a portion (operation portion) which performs key operation, andreference numeral 2602 shows a portion which performs informationdisplay (information display portion), and the operation portion 2601and the information display portion 2602 are connected by the connectingportion 2603. Further, the operation portion 2601 is provided with asound input portion 2604, operation switches 2605, and the informationdisplay potion 2602 is provided with a sound output portion 2606, adisplay portion 2607.

The light-emitting device and the liquid crystal display portion of thisinvention may be used as the display portion 2607. Note that, when usingthe EL light-emitting device to the display portion 2607, theconsumption power of the portable telephone may be suppressed bydisplaying white letters in the background of the black color.

In the case of the portable telephone shown in FIG. 21A, the ELlight-emitting device used in the display portion 2604 is incorporatedwith a sensor (a NMOS sensor), and may be used as an authenticationsystem terminal for authenticating the user by reading the fingerprintsor the hand of the user. Further, light emission may be performed bytaking into consideration the brightness (illumination) of outside andmaking information display at a contrast that is already set.

Further, the low power consumption may be attained by decreasing thebrightness when using the operating switch 2605 and increasing thebrightness when the use of the operation switch is finished. Further,the brightness of the display portion 2604 is increased when a call isreceived, and low power consumption is attained by decreasing thebrightness during a telephone conversation. Further, when using thetelephone continuously, by making it have a function so that display isturned off by time control unless it is reset, low power consumption isrealized. It should be noted that this control may be operated by hand.

Further, FIG. 21B shows an audio, which contains a casing 2701, adisplay portion 2702, and operation switches 2703 and 2704. Thelight-emitting device and the liquid crystal display device of thisinvention can be applied to the display portion 2502. Further, in thisembodiment, a car mounted audio (car audio) is shown, but it may be usedin a fixed type audio (audio component). Note that, when using an ELlight-emitting device in the display portion 2704, by displaying whitecharacters in a black background, power consumption may be suppressed.

Further, electrical equipment shown above are incorporated with a lightsensor in the light-emitting device and the liquid crystal displaydevice which are used in the display portion, and it is possible toprovide means to detect the brightness of the environment of use. Whenusing the EL light-emitting device in the display portion, it is mayhave a function that modulates the light-emission brightness accordingto the brightness of the environment of use. Specifically, this isimplemented by providing an image sensor (surface shape, linear or adotted sensor) formed by a NMOS circuit on the EL light-emitting deviceusing the display portion, and providing a CCD (charge coupled device)on the main body or the casing. The user may recognize the image or thecharacter information without trouble if a brightness of a contrastratio of 100 to 150 may be maintained as compared to the brightness ofthe environment of use. Namely, in the case the environment of use isdark, it is possible to suppress the consumption power by suppressingthe brightness of the image.

As in the above, the applicable range of this invention is extremelywide, and may be used for various electrical equipment. Further, theelectrical equipment of this embodiment may use the light-emittingdevice and the liquid crystal display device containing any of thestructures of Embodiments 1 to 5.

It is possible to manufacture a light-emitting device having a highlight extraction efficiency at a low cost and at a high yield bycarrying out the present invention. Thus, a light-emitting device whichis inexpensive but capable of displaying a bright image can be provided.Also, a low-priced electric appliance having a display portion capableof displaying a bright image can be provided by using in the displayportion the low-priced light-emitting device capable of displaying abright image.

1. A light-emitting device comprising: a display portion comprising aplurality of pixels formed over a substrate; and a driver circuit formedover said substrate, wherein said driver circuit comprises a shiftregister containing a plurality of flip-flop circuits comprisingenhancement-type n-channel thin film transistors and depletion-typen-channel thin film transistors, wherein all semiconductor elements insaid display portion and said driver circuit are n-channel typesemiconductor elements, and wherein each of said plurality of pixelscomprises a light-emitting element.
 2. A light-emitting device accordingto claim 1, wherein said substrate is a plastic substrate covered with aprotective film.
 3. A light-emitting device according to claim 1,wherein said light-emitting device is incorporated in one selected fromthe group consisting of an EL display, an image playback device, apersonal computer, a video camera, a digital camera, a mobile computer,a mobile telephone, and an audio.
 4. A light-emitting device accordingto claim 1, wherein each of said plurality of flip-flop circuitscomprises an enhancement-type n-channel thin film transistor and twocircuits.
 5. A light-emitting device according to claim 4, wherein oneof the circuits is an EEMOS circuit.
 6. A light-emitting deviceaccording to claim 4, wherein one of the circuits is an EDMOS circuit.7. A light-emitting device according to claim 4, wherein each of saidplurality of flip-flop circuits further comprises an inverter circuit.8. A light-emitting device according to claim 4, wherein said pluralityof flip-flop circuits are connected in series.
 9. A light-emittingdevice according to claim 1, wherein one of the enhancement-typen-channel thin film transistors is electrically connected with one ofthe depletion-type n-channel thin film transistors.
 10. A light-emittingdevice according to claim 1, wherein a semiconductor element in thedisplay portion has at least two channel forming regions.
 11. Alight-emitting device according to claim 1, wherein each of saidplurality of pixels comprises two semiconductor elements a switchingelement, a current control element for controlling an amount of currentto the light-emitting element, and a capacitor.
 12. A light-emittingdevice according to claim 1, wherein the semiconductor element is aninverted stagger thin film transistor including a microcrystallinesemiconductor film.
 13. A light-emitting device comprising: a displayportion comprising a plurality of pixels formed over a substrate; and adriver circuit formed over said substrate, wherein said driver circuitcomprises a shift register containing a plurality of flip-flop circuitscomprising enhancement-type n-channel thin film transistors anddepletion-type n-channel thin film transistors, and comprises aplurality of NAND circuits each comprising first and secondenhancement-type n-channel thin film transistors and a depletion-typen-channel thin film transistor, wherein a gate electrode of firstenhancement-type n-channel thin film transistor is connected to a firstoutput line, wherein a source electrode of first enhancement-typen-channel thin film transistor is connected to a ground power supplyline, wherein a drain electrode of first enhancement-type n-channel thinfilm transistor is connected to second enhancement-type n-channel thinfilm transistor, wherein all semiconductor elements in said displayportion and said driver circuit are n-channel type semiconductorelements, and wherein each of said plurality of pixels comprises alight-emitting element.
 14. A light-emitting device according to claim13, wherein said substrate is a plastic substrate covered with aprotective film.
 15. A light-emitting device according to claim 13,wherein said light-emitting device is incorporated in one selected fromthe group consisting of an EL display, an image playback device, apersonal computer, a video camera, a digital camera, a mobile computer,a mobile telephone, and an audio.
 16. A light-emitting device accordingto claim 13, wherein a semiconductor element in the display portion hasat least two channel forming regions.
 17. A light-emitting deviceaccording to claim 13, wherein each of said plurality of pixelscomprises two semiconductor elements a switching element, a currentcontrol element for controlling an amount of current to thelight-emitting element, and a capacitor.
 18. A light-emitting deviceaccording to claim 13, wherein the semiconductor element is an invertedstagger thin film transistor including a microcrystalline semiconductorfilm.
 19. A light-emitting device comprising: a display portioncomprising a plurality of pixels formed over a substrate; and a drivercircuit formed over said substrate, wherein each of said plurality ofpixels comprises a plurality of enhancement-type n-channel thin filmtransistors and a plurality of depletion-type n-channel thin filmtransistors, wherein all semiconductor elements in said display portionand said driver circuit are n-channel type semiconductor elements, andwherein each of said plurality of pixels comprises a light-emittingelement.
 20. A light-emitting device according to claim 19, wherein saidsubstrate is a plastic substrate covered with a protective film.
 21. Alight-emitting device according to claim 19, wherein said light-emittingdevice is incorporated in one selected from the group consisting of anEL display, an image playback device, a personal computer, a videocamera, a digital camera, a mobile computer, a mobile telephone, and anaudio.
 22. A light-emitting device according to claim 19, wherein asemiconductor element in the display portion has at least two channelforming regions.
 23. A light-emitting device according to claim 19,wherein each of said plurality of pixels comprises two semiconductorelements a switching element, a current control element for controllingan amount of current to the light-emitting element, and a capacitor. 24.A light-emitting device according to claim 19, wherein the semiconductorelement is an inverted stagger thin film transistor including amicrocrystalline semiconductor film.
 25. A light-emitting devicecomprising: a display portion comprising a plurality of pixels formedover a substrate; and a driver circuit formed over said substrate,wherein each of said pixels comprises an SRAM formed by a plurality ofenhancement-type n-channel thin film transistors and a plurality ofdepletion-type n-channel thin film transistors, wherein allsemiconductor elements in said display portion and said driver circuitare n-channel type semiconductor elements, and wherein each of saidplurality of pixels comprises a light-emitting element.
 26. Alight-emitting device according to claim 25, wherein said substrate is aplastic substrate covered with a protective film.
 27. A light-emittingdevice according to claim 25, wherein said light-emitting device isincorporated in one selected from the group consisting of an EL display,an image playback device, a personal computer, a video camera, a digitalcamera, a mobile computer, a mobile telephone, and an audio.
 28. Alight-emitting device according to claim 25, wherein a semiconductorelement in the display portion has at least two channel forming regions.29. A light-emitting device according to claim 25, wherein each of saidplurality of pixels comprises two semiconductor elements a switchingelement, a current control element for controlling an amount of currentto the light-emitting element, and a capacitor.
 30. A light-emittingdevice according to claim 25, wherein the semiconductor element is aninverted stagger thin film transistor including a microcrystallinesemiconductor film.